“We have to call this what it is,” Volodymyr Zelensky said, late last month, a few days after Vladimir Putin had ordered the invasion and conquest of Ukraine. “Russia’s criminal actions against Ukraine show signs of genocide.” President Zelensky, who lost family members during the Holocaust, and who also happens to have a law degree, sounded suitably cautious about invoking genocide, and he called for the International Criminal Court in The Hague to send war-crimes investigators as a first step. But such investigations take years, and rarely result in convictions. (Since the I.C.C. was established in 1998, it has indicted only Africans; and Russia, like the United States, refuses its jurisdiction.) The only court that Zelensky can make his case in for now is the court of global public opinion, where his instincts, drawing on deep wells of courage and conviction, have been unerring. And by the end of the invasion’s second week—with Putin’s indiscriminate bombardment of civilian targets intensifying, and the death toll mounting rapidly; with more than two and a half million Ukrainians having fled the country, and millions more under relentless attack in besieged cities and towns; and with no end in sight—Zelensky no longer deferred to outside experts to describe what Ukrainians face in the most absolute terms. “I will appeal directly to the nations of the world if the leaders of the world do not make every effort to stop this war,” he said in a video message on Tuesday. He paused, and looking directly into the camera, added, “This genocide.”